Electrical fuse



H. A. TRIPLETT ELECTRICAL FUSE May 9, 1939.

Sheets-Sheet 1 Filed Oct. 18 1937 www. H" II...

/ll'lll y 9, 1939- I H. A. TRIPLETT 2,157,152

ELECTRICAL FUSE Filed Oct. 18, 1937 5 Sheets-Sheet 3 Patented May 9,1939 [UNITED STATES PATENT OFFICE ELECTRICAL FUSE Hugh A. Triplett,Wilmette, 11]., assignor to Schweitzer & Conrad, Inc., Chicago, 111., acorporation of Delaware Application October 18, 1937, Serial No. 169,611

18 Claims.

Y phases of the invention, wherever useful.

According to present practice, distribution systems usually operating atfrom 2,300 volts to 15,000 volts are protected by fuse devices ofvarious construction and variously designated. Be-

cause of the large number required in a system of any extent, the itemof initial expense and maintenance is a paramount consideration. The airbreak fuse has chiefly for this reason been widely adopted. Due to thelocation of these devices remote from the central station busses andwith the reactance of the lines intervening, the amount of current thatmust be interrupted is limited to values which make air break fusesoperating upon the expulsion principle fairly satisfactory. These fusesare disposed in or on various forms of mountings.

The typical commercial embodiment of the expulsion fuse early took theform of a tube of insulation with ferrules upon-the ends, and a closurefor one end with the fusible portion of the link disposed adjacent saidclosed end. Great numbers of devices of this character have beenemployed, and are still in commercial use.

It was early recognized by my assignee that the simple expulsion fuse,while, in general; it operated fairly satisfactorily on relatively heavyoverloads, came into difliculty on low overloads, as the expulsive forcewas not great enough to propel the link and cause separation of the ter-40 minals, and interruption. Destruction of the device results. Fuses oflarge current carrying capacity are less subject to this particulardifliculty because the blowing of a large capacity link releases enoughenergy to create a satisfactory expulsive effect. My present inventionis particularly useful for 10w amperage fuses.

Another difficulty with fuses of this type has been the uncertainty asto time-current characteristics, particularly on low amperage fuses. A

further uncertainty resided in the uncertain lengths of arcing time offuses as heretofore constructed. 1

The prior United States patent to Conrad, No.

1,466,423, largely overcame these difficulties by placing the fuse linkunder spring tension and surrounding the fusible element with a cork.Employment of spring tension was practicable because a method ofrelieving the fusible element from stress and possible injury by thespring load had been satisfactorily worked out, i. e., the use 5 of theso-called strain wire. Upon the occurrence of overload great enough tocause fusing of the fusible element, the terminals were promptlyseparated far enough to insure expulsive action and interruption of thecurrent flow. 10

I have conceived the expulsion fuse as being, of necessity, a dual rangedevice. According to my conception of the ideal expulsion fuse, it musthave the capacity for operating in one fashion upon low overloads, andin another fashion upon high overloads, but these two modes must be socoordinated as to be mutually helpful or to overlap in producing thedesired result In brief, the two modes of operation must work in thesame general direction, so that in the intermediate 0 range when bothactions occur, they may overlap and work to the common end; 'The deviceof my present invention is designed to do this.

In considering various forms of fuse devices upon the market, I haveconceived the possibility 25 of incorporating within the fuse linkitself the principle of operation of the aforesaid United States Patentto Conrad, No. 1,466,423, so that the resulting device employing suchlinks will have the desired plural range action and suitable 0time-current characteristics, short arcing time, etc.

One of the primary objects of my invention is to provide a fuse link foruse in fuse holders of various forms or for various mountings to con- 35stitute the same as plural range fuse devices with suitablepredeterminable time-current characteristics and arcing time for eachdesired capacity.

For the accomplishment of this object and other objects, I have deviseda form of link, which I 40 term a universal link, having such structuralAnother object of the invention is to provide an improved form offusible element for the link, such element having a high temperaturemetal which is relatively free from corrosion, and has long life,accuracy in time-current characteristics, and the ability to standmomentary surges without deterioration.

A further object of the invention is to provide a fusible element whichshall be suitable for withstanding the tension required in spring loadedor weight-loaded cutouts, such as automatic dropouts or reclosing fuses,and yet be satisfactory for use in cutouts putting no tension on thelink.

Accuracy in blowing time of fuse links would be of little or noimportance if heavy short-circuit currents were possible at the pointswhere most cutouts are installed. The fact is that on most systems, andparticularly rural systems, heavy short-circuit currents are theexception rather than the rule. Therefore, this means that most cutoutssold are subjected to an interrupting duty which is out on the long timeblowing end of the time-current curve. Out on the low current end of thecurve, reliable accuracy in blowing time andcurrent is essential if apower company insists on good operating results. By good results, I meanthat the accuracy of the fuse link is such that its blowing can be socoordinated with the circuit breaker at the head of the feeder, and soco-ordinated with any other fuse in sequence on the line, that when afault occurs, on the load side of the cutout, a fuse link will isolatethe fault in time to prevent these other fuses or breakers from openingand thus dropping the load in adjacent territory. This requires, in afuse link, both accuracy in time-current characteristics and reliableshort arcing time. No matter how accurate the melting of the link, longand indefinite arcing time will undo the benefit of such accuracy bycausing other devices in seically weak with respect to spring tension,and

entirely unsuited to be installed in a cutout employing a tensioningspring, the fuse oi the present invention permits the use of a heavierwire which is entirely adequate in tensile strength. The link of thepresent invention will melt and part at the same overload or faultcurrents which would melt the wire of hairlike proportions. The fuse ofthe present invention will withstand the spring tension which is foundin all of the cutouts of my assignee and in the cutouts of the newdropout type which are coming into the market.

In carrying out this phase of the invention, I" employ a pair of wires;preferably of nickelchromium alloy, having hooked engagement with eachother. The wires are of adequate mechanical strength to resist thenecessary spring tension but the hooked connection will readily yieldunder the spring tension which is provided by straightening out thehooked or bent parts of one or both of the wires. By' provision of amolded bead of a low melting point metal or alloy which encases orembeds the hooked engagement, the Pulling apart of the hooked engagementis prevented until the bead softens suiiiciently to permit the end ofthe hook to swing about through the body of the low melting point metaland straighten out sufliciently to. pull clear of the cooperatinganchorage.

A further object of this invention is to provide a fuse link which has avery sharp melting and parting point on the temperature curve, that is alink which does not soften and stretch and thus reduce its cross-sectionas the temperature closely approaches the definite melting point. In thepresent construction, the bead of tin or other low melting pointmaterial either allows the hooked engagement to pull apart or it willnot permit the bent portion of the hook to straighten out at all. Thepresent fuse link, therefore, does not result in a progressivelengthening of the fusible section, as would be the case if the twowires were soldered together or otherwise connected through the body oflow melting point metal.

Another object of the invention is to provide a fuse link with a noveland distinctive form of time-current characteristic curve, asillustrated in exaggerated form in Figure 4. A fuse having such acharacteristic curve, that is, with the short and medium time blowingpoints elevated permits the momentary surges or transients, such aslightning or induced current, to pass through the device without meltingof the bead. There is, therefore, less cumulative effect of repeatedsurges which might otherwise cause the link to melt and part at normalload current. In that part of the curve corresponding to long timeblowing there is a relatively sharp dip beyond the duration time ofsurges and transients. Being at the long time end of the curve, andbeing a substantial drop in the curve, it serves as a protection againstdetrimental thermal effect in the transformer to which this link isapplied as a protection. It is known that long continued overload of theorder of 50% or possibly 100% on the transformer results in destructionof the insulation. It is therefore desirable to have the long time endof the curve as low as possible with respect to the normal load currentof the transformer while the medium and short blowing time of the curveshould be higher with respect to the normal load current of thetransformer. It is desirable, therefore, that these two sections of thecurve be joined by a section which is as nearly vertical as it ispossible to provide. This object is particularly desirable for fuses ofthe order of one to two ampere ratings which blow on currents rangingfrom one to three or four amperes.

In addition'to the foregoing objects there are other and numerousobjects of the present invention which will be apparent from thefollowing detailed description and the appended claims.

Now in order to acquaint those skilled in the art with the manner ofconstructing and operating a device in accordance withmy invention Ishall describe, in connection with the accompanying drawings, severalspecific embodiments of the invention.

In the drawings, the same or similar reference characters designate thesame or similar parts, throughout.

Figure 1 is a side elevational view of a low amperage fuse link of theorder of one to two amperes, the specific fuse link shown is a twoampere link;

Figure. 2 is a vertical, longitudinal sectional view through the fuselink of Figure 1, taken along the line 2-2;

Figure 3 is a view of the fuse link and terminals taken at right anglesto the view of Figure 2;

Figure 4 is a diagram illustrating the type of time-currentcharacteristic curve which is secured by the fuse of Figure 1;

Figure 5 is a time-current characteristic curve showing the relationbetween current in amperes and time in seconds to blow fuses of thepresent invention plotted on a logarithmic scale; and

Figures 6 through 13 show, at an enlarged scale, different embodimentsof bead-construction.

Referring first to Figures 1, 2, 3, and 6, I have shown a fuse link Iwhich necessarily involves three essentials. First, a terminal portion2, such as is suitable for attachment to one electric terminal andsupport, a fusible section 3 (Figure 2), and a flexible lead andterminal portion 4 for' making connection with another elec- 7connector, the outer end of which as shown at 6, is tinned to hold thestrands together. It will be observed that the terminal portion 4 isprovided with a collar member I which has an intermediate portion 8 thatis pinched or flattened upon the body of the lead 4 and which isprovided with a flared or conical wedging contact IQ for engagement in acooperating stationary wedging contact such as shown in Patent No.2,091,453, of Allan Ramsey.

The upper terminal 2 comprises a cylindrical stud member I 3 (Figure 3),the outer end of which is threaded at l4. The intermediate portioncomprises a flange [5 which may represent the original diameter of thestock from which the stud is out, as by a screw machine. Adjacent theflange I 5 there is a groove l6 and beneath the same a knurled portionH. The inner end of the stud 13 comprises a tubular socket portion l8into which is inserted. the upper end of the fuse wire l9 of the fusiblelink 3. The tubular portion I8 is then flattened or pinched upon the endof the wire to make good electrical and mechanical connection with saidwire l9.

The threaded stud I3 is adaptable to a wide variety of situations formaking connection between the link and a suitable terminal, eitherstationary or movable, as the case may be. For connection with astationary mounting wherein an annular seat and a cooperating cap orclamp argemployed, a flanged 'head 29 is provided. This flanged headcomprises a tubular sleeve or shank internally threaded to cooperatewith the threads l4 of the stud l3 and having its upper end flanged orflared out as indicated at 21 as by a spinning operation. Where theannular seat is of greater extent than would be suitably engaged by' theflange 21, a dished washer 23 is provided (Figure 1), this washer beingpassed over thelink from the opposite end and resting under the flange21. The end of the stud I3 is substantially flush with the top of theflange 21 and provides a'good clamping surface additional to the topofthe conical flange 21.

The wires l9 and 29 have hooked engagement at 22, as shown in detail inFigure 6. A molded bead 23 of low melting point metal or alloy, such forexample, as solder or tin, is molded on the hooked engagement 22 andembeds the ends of the wires l9 and 20 where they make engagement. Thelower end of the wire 20 is folded back on itself like the upper end ofthe wire l9 and is disposed in a tubular fitting 29, the upper end ofwhich provides a socket 30 which is flattened upon the end of the wire20 to grip it mechanically and to make connection electrically. Thelower end of the fitting 29, which is preferably made of a piece ofcopper tubing or the like, is similarly pinched or flattened upon theupper end 40 of the flexible lead 4.

The fitting 29 therefore forms a coupling or junction member between thelower end of the fusible element 3 and the lead 4. It also forms ananchorage for the tension spring 33, which has its upper coil flattenedagainst the flat sides of the pinched socket 30 and is prevented fromdisengagement by the shoulders 34 of the flattened part of the socket32, since the flattened portions of the sockets 30 and 32 are sodisposed that their planes are substantially at right angles to eachother.

The spring 33 has its opposite and anchored directly to the flattenedcollar 35 which is pinched upon the flexible lead 4. Indirectly, thespring is anchored to the cap or plate 36 through the medium of thefitting I, which has its adjacent end 31 in engagement with the plate orcap 36.

The margins of the plate or cap 36 are so formed as to center it uponthe lower end of a fiber tube 38. The upper end of the tube 38 issecurely bound to'the upper terminal stud [3 in axial alignmenttherewith and rigid for both rotary or axial motion with respectthereto. This engagement is secured preferably by wetting the end of thefiber tube 38, pushing it over the knurled portion l1, and thenshrinking the end into the groove under the flange l5. Such shrinkagemay be facilitated by pinching.

It will be observed that the spring 33 does not apply any tension to theportion 40 of the flexible conductor 4 between the terminal 29 and thecollar 35. Any desired tension may be applied to the flexible lead 4externally, either by springs in the housing or by the lineman inrefusing the.

housing, without imposing on the link 3 any stress in addition to thatalready imposed by the spring 33 unless this stress imposed by thespring 33 is exceeded. This type of spring arrangement and fasteningtherefor provides a non-cumulae tive type of replaceable spring link. Itconstitutes a distinct advance in the art. However, the non-cumulativearrangement 'of the spring 33 forms no part of my invention. It isdisclosed and claimed in the copending application of Lindell, SerialNo. 70,280, filed March 23, 1936, and assigned to the assignee of thisapplication.

The spring 33 is arranged to place the link 3 under a tension which, inthe present instance, is of the order of seven pounds. In the S 8: Ccutouts of the type shown in United States Patent 1,818,382, the tensionof the spring which tends to separate the terminals of the fusible linkranges from to 12 pounds.' This amountof tension is necessary in view ofthe unavoidable mass of the terminal and cable assembly which isrequired to extend the rating of any particular .cutout 'to includelinks of higher ampere rating,

say up to 60 amperes.

Now inasmuch as the present link is designed and adapted to be insertedin cutouts of that type as well as in other forms of mountings, fusetubes and the like, it is desirable that the fusible element be capableof withstanding spring tension of that order, that is, from 10 to 12pounds' I have provided the hooked engagement 22 and the soft metal bead23 as a means for permitting the employment of wires i9 and 20, which.are ample in cross section and mechanical strength to withstand springloads or other loads of from 10 to 12 pounds. The wires 59 and 2t willnot fuse at from 1 to 3 or 4 amperes, which is the definite overloadvalue at which the fuse shall open, but the hooked engagement, combinedwith the minimum spring tension, is designed to do this under thecontrol of melting of the molded metal bead 23. That is to say, thewires it and 20 must maintain good mechanical strength throughout thelife of the device and must maintain substantially unchangedcross-section. These wires are made of metal which does not corrode,deteriorate due to oxidation, or is not otherwise attacked byatmospheric ingredients or components. Preferably, I use an alloy ofnickel and chromium which appears on the market under the trade name ofChromel A. Obviously, I do not wish to be limited to this specificmaterial, as any other metal which has noble characteristics may beemployed.

The critical point of the construction resides in the straightening out,or release, or pulling apart of the hooked connection.

I am aware that it is old to have parts soldered together or heldtogether by a solder or soft metal rivet or the like, but these devicesare subject to change in characteristics due to an approach to themelting point and a recession therefrom. In the 1 ampere fuse size Iemploy wires for 1 ampere rating of the order of 0.016 inch in diameter,and for a 2 ampere rating of the order of 0.018 inch in diameter of theaforesaid material, and where the total length of the fusible linkbetween the tubular end portions l8 and 30 may be of the order of 1inch.

The hooked engagement 22 is preferably that shown in detail in Figure 6,wherein the wire I9 has a closed loop or eye 42 formed upon the endthereof, this eye being, for example, circular and formed by bending thestdck adjacent the end into a circular annular loop, with the end of thewire, as at 43, brought parallel with the main body thereof, and weldedor otherwise secured thereto. The wire 20 likewise has a loop 44 ofsimilar configuration, but having its end 115 free. A bead of lowmelting point metal, for example, tin, solder or the like, is then castabout this hooked engagement, and this device thereupon forms amechanical relay controlled by temperature. Obviously, instead offorming one loop completely closed by welding the end 43 as shown inFigure 6, the ends of both wires may be left open, as shown in Figure'7, at 22'. In the sizes of wire shown without the metal bead 23 castin'place, a tension of only 3 to 4 pounds is sufficient to straightenout the hooked engagement sufli'ciently to allow the wires i9 and 20 topull apart. But with the head 23 in place the hooked engagement isstronger than the main part of the wires 89 and 20, until it is softenedby heat. When the bead 23 is softened by heat generated in the wires l9and 20 by current flow, the Wires i9 and 20 can be pulled apart bystraightening out the hooked engagement with a force of 7 pounds orless. The conductivity of the bead 23 surrounding the hooked engagementis so great that this part of the fusible element does not becomes'ufiiciently elevated in temperature by current flow but heat isgenerated in the intermediate parts of the wires i9 and 20, that is,between the bead 23 and the terminals 88 and 30, and the heat isconveyed to the bead 23, bringing it up to a temperature where itsoftens sufficiently to permit the tension of the spring to separate theparts. The wires i9 and 2t) will not soften sumciently under heat tocause any weakening thereof short of approximately 800 C. to 900 C., butthe metal bead 23 will soften between 200 C. and 300 C. There is,therefore, a wide difference in the effective temperatures of the twoparts of the fusible link.

It is to be understood that the amount of spring tension which is placedupon the fusible link affects the time-current characteristic of thelink. That is to say, if the spring tension is excessive, obviously itwill break the link without any current flow. If the current flow isgreat enough to affect the temperature of the link, it

- will affect the mechanical strength, even though the link be but astraight wire. If the wire alone be considered, no appreciable weakeningin mechanical strength will be caused by current flow until the wirereaches a critical temperature, whereupon the spring tensionwill have amarked effect upon the time-current characteristic. The fusible element3 shownin Figures 2, 3, and 6 of the drawings is a compound device inwhich it is intended, as hereinabove stated, to secure an offset in thetime-current characteristic curve which is idealized in Figure 4.

In that curve I have shown only the general contours and not absolutevalues. ous full line curve shows the characteristics desired. Thedot-and-dash curves indicate continuations of the two independent curveswhich are combined by my invention. The part of the curve running from Pto M is a part of a curve for one capacity of fuse. The part of the fullline curve running from N to Q is part of the curve of a lower capacitylink. Assume that the line MN is a substantially vertical line and thatthis line is placed at substantiallythe second value, for example, itwill be assumed that for values of current greatly in excess of thenormal load current, the blowing time is relatively short, but a markedincrease of current is required if the fuse is to blow in less than 60seconds. Within this range the wire H3 or 20 itself melts. Within therange N-Q the bead melts and releases the link. It is desirable thatthis should occur at as small an increase above normal load current asit I is possible to secure in order that apparatus on the line, such astransformers, will not be subjected, for any appreciable period of time,to values of current flow substantially in excess of the normal rating.

In practice it is not possible to have as sharp a junction as indicatedby the vertical line MN in Figure 4. In Figure 5 of the drawings, I haveshown the shape of actual curves as plotted from tests made on fuses ofthis character. The curves, marked Nos. 1 and 2, are curves representingthe performance of one and two ampere fuses constructed in accordancewith the disclo sure of Figures 1, 2, 3, and 6 of the drawings. It willbe observed that these curves are of the general shape indicated byFigure 4, the relatively sharp dips indicated in the region MN' showingthe pronounced efifectwhich is produced by the introduction of the beadand hook construction heretofore described.

The continu- As above indicated, the hook and bead principle may beembodied in quite different forms. For example, in Figure 6, the hookedfree end 45 may be considered as a lever hinged to the main shankportion of the wire 20 with a predetermined friction at the pivot asrepresenting the force required to swing it into the unhooking position.Obviously, as indicated in Figures 10 and 11, the principle would not bechanged by hav-' ing the free end 45' pivoted to the main shank portionof the conductor 20, for example, without friction. In other words, theend 45', which constitutes a lever, might be pivoted to the main shankby an actual pivot joint giving a known leverage of relatively highvalue. The real resistance to unhooking of the connection of these twowires resides in the molded head 23. In order to move to an unhookingposition, the free end 45 must swing sidewise through the metal of thebead. To permit this the metal of the bead must be soft enough to allowthe arm 45' to swing therethrough. This mode of operation is entirelydifferent from prior devices, in which a straight wire or a wire bentinto zig-zag or coiled form is embedded in a bead, since according tothat construction, spring tension allows a slow creepage or lengtheningof the link to occur, thereby changing its ratingand rendering thedevice unreliable. In the present case, even if the free lever-like end45' should begin to swing and then be halted, no appreciable lengtheningof the wire 20 or of the link 3 as a whole could be detected. Hence, thetime-current characteristic of the link would not be changed, andthatwould be true of any position of the. wire 45' short of allowing anactual unhooking or slipping through the eye 42.

In Figure '7, I have indicated open hooks on both the wire I9 and thewire 20 to give the hooked connection 22'. In practice it is notnecessary or doesirable to have more than one of the wires provided withan open hook, inasmuch as there is a tendency for the bead 23 to berotated and, as the bead is oblong, it mightcome into a position in thefiber tube 38 which would interfere with its free rotation andexpulsion. Furthermore, contact of the head 23 with the inside of thefiber tube is not desirable, as it tends to alter the time-currentcharacteristics of the device.

In Figures 8 and 9, I have shown the eye 42 as provided with a smallerroller 41 of a definite exterior diameter, so as to control accuratelythe pivotal point about which the free end 45 of the wire 20willrotatefi By thus providing a definite radius and conforming the endof the wire 20 to that radius, a snug and certain fit may be obtained,showing very definitely the yielding point of the link.

Also, it is to be understood that instead of the two wires directlyhooking with each other, they .may hook with an intermediate link whichprovides either the hook portion or the eye portion. Such a constructionis shown in Figures 12 and 13 of the drawings. As there illustrated, thewires I 9 and 20 terminate in eyes 49 and 50 which may be formed bysuitably bending the adjacent ends of the wires I9 and 20 back andwelding them to the shank portions, as indicated at 5| and 52respectively. The eyes 49 and 50 are interconnected by a link 53 which,may comprise a generally c-shaped member. The entire assembly isembedded, as shown, in the bead 23 for the reasons set forthhereinbefore.

the wires I9 and 20, each may be chosen, as to material, with respect toits separate function. That is, the wires I9 and 20 may be chosen withrespect to the tension stress applied thereto and the means employed forfastening them in the sockets I8 and 30, Figure 3, while the link 53 maybe composed of a difierent kind or size of material or both and withreference to the timecurrent characteristics desired and its relation tothe melting of the bead 23.

In the operation of blowing of a fuse link in a fuse housing, such as anexpulsion tube employing the fuse link-shown in Figures 1, 2, and 3,there are two ranges of operation wherein different modes of action aresecured, all to. a common end of accurate predetermined operation.

Assume that the excess current is in the lower ranges wherein the wiresI9 and 20 are heated by the fiow of current but not to the point wherethese wires lose their mechanical strength, that is, in a region to theright of the hump in the curves indicated at MN in Figure 5. The wiresI9 and 20, transmit heat to the low melting point bead 23 and, if thecurrent is maintained for a period of time which will permit the bead tobecome softened to the point of allowing the end 45 of the wire 20 toswing about through the body of the bead and become unhooked, the fusethereupon operates to interrupt the circuit. Inasmuch as certain typesof expulsion fuse housings are provided with springs which exert a pullof the order of 10 to 12 pounds, whereas the spring 33 has a pull of theorder of 7 pounds, the total stress upon the fusible link is only 10 to12 pounds. Hence, no substantial deviation from the type of curve shownin Figure 5 is occasioned by this form of mounting.

For higher values of current fiow above the hump indicated at MN, Figure5, the fiow of current tends to soften the wires I9 and to such anextent that they yield mechanically before sufficient heat istransmitted to the bead 23 to cause softening of the same, and fusion ofthe bead is not depended upon to secure opening of the circuit. In thisevent the wire I9 or 20 pulls apart, due to the spring tension, and thecircuit is opened as above described, with the combined action of thesprings and the gases formed upon blowing of the fusible link.

The fiber tube 38 is not intended to be expelled with the fuse terminal29, as it is anchored firmly to the stud member I3. The tube 38 seryesthe useful purpose of confining the gases and assisting in the expulsiveeffect, particularly on the lower current values. Also, it protects theinside of the permanent fuse tube from injury by the arc. Also, itserves to assist in evolving deionizing gases, as it appears that thedecomposition of the fiber by the arc is helpful in the action ofdeionizlng the are by driving gases evolved from the walls of the tubeendwise of the arc to sweep out the ionized product and metal vapors.The sleeve 38, while it is preferably made of plain gray fiber, may bespecially constructed to assist in the evolution of gases as byimpregnating the same with a liquid or solid arc extinguishing medium,as disclosed in the United States patent to Ringwald, Reissue No.19,097.

From the above it will now be apparent that I have provided a fuse linksuitable for employment in a wide variety of mountings, in which thereis a predetermined spring tension to controlthe time-currentcharacteristic according to a desired mode of operation. This springtension is great enough for the very low ampere fuses, such as one ortwo amperes, to overcome the hooked engagement of the fuse wires whenthe bead melts. Mere melting of the bead does not release the hookedconnection of the wires, and this spring tension is therefore necessaryto secure opening of the circuit for current values which are lower thanthose which would actually melt the wires, such as the wires i9 and 2b.In this manner it is possible to secure a very delicate response to lowcurrent values while employing parts of ample mechanical strength anddimensions.

I believe that the hook and bead principle is broadly new. I am awarethat it has been attempted to hold parts together by solder, wax andvarious other expedients, but in all of the structures with which I amfamiliar, there is no positive mechanical engagement such as I haveobtained by the use of the hook and eye, independently of the bead orsolder.

Numerous other advantages in manufacture and operation will be apparentto those skilled in the art.

I do not intend to be limited to the details shown and described.

I claim:

1. In an electric fuse, a fusible current carrying element ofpredetermined rating comprising a pair of wires of relatively highmelting point having portions coupled mechanically by hooked connection,and a body of metal fusible at a relatively low temperature and holdingsaid hooked connection against disconnection by bending a hooked part ofthe wire, said wires being fusible by large increase of current, andsaid body of metal being fused by current flow insufficient to melt saidWires when continued over a period of time.

2. In a fuse of small current carrying capacity adapted to withstandspring tension, a pair of wires of relatively high mechanical strengthand relatively high melting point having hooked connection, and a headof meal of relatively low melting point embedding said hooked connectionof said wires.

3. In a small capacity fuse element adapted to be placed undersubstantial tension, a pair of nickel-:chromium alloy wires havinghooked connection with each other, and a bead of metal comprising tinembedding said hooked connection.

4. In a device of the class described, a fuse element comprising a pairof wires of high tensile strength, high melting point and resistant tocorrosion, a closed loop formed on one wire, an open loop on the otherwire hooked through said closed loop, and a bead of low melting pointmetal embracing said open loop to keep it from opening by tensionimposed upon said elements until the heat from said wires softens themetal of said bead.

5. In combination in a fuse, a pair of wires of high tensile strengthand small cross section having hooked connection, and a bead of tinformed about said hooked connection and being subject to being softenedby the heat of said wires to release said hooked connection undertension.

6. In a fuse of a given ampere rating, the combination of a conductinglink comprising a member having an eye, a member having a hookcooperating with said eye, and a body of low melting point metalcoupling the open side of the hook to the shank thereof, at least one ofsaid members being heated up by current flow in exawaits cess of saidrating to raise said body of metal substantially to its melting pointwhereby it loses its coupling effect, and a spring imposing sufficienttension upon said members to pull. the hook out of the eye when the hookis freed by softening of said body of metal.

7. In combination in a fuse, a fusible link comprising a pair of hightensile strength wires of small cross section having hooked connection,a bead of low melting point metal embedding said hooked connection, andmeans placing said hooked connection under predetermined mechanicaltension sufficient to straighten the hooked part of one wire when saidbead is melted.

8. A fusible link comprising a pair of corrosion resisting wires ofrelatively high tensile strength having hooked connection with eachother, and a soft metal body of relatively low melting point in goodthermal contact with at least one of said wires preventing unfolding ofsaid hooked connection.

9. A fusible link comprising a corrosion resisting wire of relativelyhigh tensile strength and high melting point, said wire having a hookformed in one end thereof, an anchorage which said hook engages, and abody of relatively low melting point metal which holds the hook fromstraightening out and releasing itself from the anchorage, said body ofmetal being in good heat conducting relation to said wire to be heatedthereby upon the flow of abnormal current through the link.

10. As an article of manufacture, a fuse link comprising a conductorhaving a fusible portion comprising a corrosion resisting wire ofrelative ly high tensile strength and high melting point, said wirehaving a hook formed in one end thereof, an anchorage which said hookengages, and a body of relatively low melting point metal which holdsthe hook from straightening out and releasing itself from the anchorage,said body of metal being in good heat conducting relation to said wireto be heated thereby upon the flow of abnormal current through the link,means carried by the link for imposing a predetermined tension upon saidfusible parts great enough to bend the hook and release it from theanchorage when the body of metal is melted, and releasable terminalmeans by which the link is supported for connecting said link in anelectric circuit to be protected.

11. The combination of a high tensile strength and high melting pointconductor having a hook which is adapted to sustain a tension less thanthat required to cause the conductor to part, a cooperating anchormember with which said hook is in hooked engagement, and a mass of lowmelting point metal for holding the hook against opening and forimproving the conductivity of gle joint between the hook and the anchormem- 12. In combination in a fuse of low but predetermined time-currentrating, a pair of members having hooked connection capable of sustaininga tension of approximately three pounds before they will disconnect, aspring operatively connected to said members and exerting a tension uponsaidmembers of approximately seven pounds, and a fusible mass of meltingpoint substantially lower than the melting point of either of saidmembers for reinforcing said hooked connection to make it capable ofresisting a tension substantially in excess of ten pounds.

13. A fuse of two or three amperes or less continuous current rating,comprising a pair of of withstanding said pull while carryingcon-9,157,152 terminals, a link comprising a pair of nickelchromium wireshaving hooked connection with each other capable of withstanding a pullof approximately three to four pounds, said wires themselves beingcapable of withstanding a pull of more than ten to twelve pounds andcapable tinuously a current substantially twice the continuous ampererating, a spring operatively connected to one of the terminals to placesaid link under a tension of approximately seven to eight pounds, and alow melting point connection for reinforcing said hooked connection tomake it capable of withstanding continuously a pull of more than ten totwelve pounds.

14. In a fuse device, a first strand anchored at one end and having aloop at the other end, a

second strand substantially in alignment with the first strand andhaving aportion extending through said loop and carried back to the bodyof said second strand whereby said strands have a hooked engagement, 8.body of low melting point metal holding the end and the body of thesecond strand together, and means connected to said second strandplacing said strands and said hooked engagement in tension and tendingto swing said end from said body of the second strand to unhook thesecond strand from the first strand.

15. In a fuse, a pair of wires of relatively-high mechanical strengthand melting point, a lever pivoted on one end of one of said wires, aloop at one end of the other of said wires interfltting CERTIFICATE OFPatent No. 2,157,152.

with said lever, and a bead of relatively low melting point metalembedding said lever and said' loop.

16. In a fuse, a pair of wires of relatively high mechanical strengthand melting point, a roller carried by one of said wires, a hook forminga part of the other of said wires and engaging said roller therebyproviding a mechanical connection between said wires, and a bead ofrelatively low melting point metal embedding said roller and said hook.

17. In a fuse, a pair of wires of relatively high mechanical strengthand melting point, each of said wires terminating in a loop portion, alink joining said loop portions, and a bead of relatively low meltingpoint metal embedding said loop portions and said link.

18. In a fuse adapted to withstand spring ten- ,sion, a pair of wires ofrelatively high mechanical strength and melting point having amechanical connection therebetween, and a bead of relatively low meltingpoint metal embedding said connection and arranged and adapted to act ata mechanical advantage therewith to prevent separation of said wires onapplication of said spring tension in such manner that stress is nottransmitted directly therethrough, said wires fusingunder high currentconditions to open the circuit and said bead softening under low currentconditions to permit. separation of said wires to open the circuit.

HUGH A. 'I'RlPLE'I'I'.

CORRECTION.

May 9, 1959.

HUGH A. TRIPIIETT It is hereby certified that error appears in theprinted specification of the above numbered patent requiring correctionas follows: Page 6, first column, line 1 .3, claim 2., for the word"meal" read metal; and-that the said Letters Patent should be read withthis'correction therein that the same may conform to the record of thecase inthe Patent Office.

Signed and sealed this 11th day of July, A. D. 19 9 (Seal) I HenrVanA'rsdale Acting omnissioner of Patents.

